My commuter bike is setup as an urban runaround with the stock Big Apple 1.9".
I may be changing my commute from 30min urban to 50min with a mix of urban and very dark rural lanes. My BAs are pretty worn out so I'm considering a change.
Does anyone have any recommendations for a quicker tyre. Will 1.5" slicks be any quicker than 1.9 BA?
I have some studded tyres for icy conditions so these will be mostly for cold/wet dark use in winter as well as rest of the year.

I predict you will get to work no sooner changing to slicks, but you'll be 0.1 mph faster between lights and stop signs.

You might look at something like a Serfas Barrista, but it might be too skinny for your rims.

I like specialized fatboys myself. I beleive they are 1.5". I don't have any experience with big Apples to compare them to.

I switched from 2.0 Big Apples to 1.5 Panaracer Paselas -- much lighter, livelier, and they certainly feel faster.

I tried Bontrager Hank 2.1 slicks, but didn't like the heaviness; settled for Panaracer RiBMo 1.5s, which I like better.

Will be going to 1.9 studded tires when we get some ice on the roads. Expect to be hatin' on them aside from when they actually keep me upright...

Do you have a budget in mind? The Marathon Supreme (if you've been satisfied with Schwalbe) in a 26x1.6 might be just the ticket, but it's not a cheap tire.

Pasela TG folding 26 x 1.26, with Continental Race 650 Lite tubes. Being a very light combo, they accelerate fast. Cruise speed should come out similar to other tires with light, supple casings.

Conti SportContact 1.6

Yep. I was just about to recommend these. I've been using them for about 4 months, and they have bee great.

I roll Vittoria Randoneur Pro's (26 x 1.5) part of the year, excellent puncture resistance, surprisingly fast. Most of the time I'm on 26 x 1 & an 8th Conti Gatorskins though. I recommend both.

What width rim are you using with the 26x1&1/8? I'm trying to figure out how skinny I can reasonably go on 20mm rims.

For a 1.25" tire, the Forte Metro K is fairly light, Kevlar belted and inexpensive. https://www.performancebike.com/bikes...8_20000_400237

Compass Tires 26" x 1.75"

I'll take a look tomorrow while I'm doing some work on my bikes. I've had them on several different rims, usually pretty wide ones like Sun Rhino-Lites and a Sun FL-18, along with a Mavic rear wheel. They do just just fine with the wider rims for what that's worth.

Specialized Armadillo MTB Slicks

Anything skinner, lighter, and higher pressure will "feel" faster, but actual differences on a commute route (what with lights and all) will be negligible.

Go for it.

Myself I like the bontrager hank (2.2" BTW) for my commute they are a little heavy but they roll smooth and fast for being a fat tire (I normally don't feel right riding on anything under 1.95") and I general keep pace with my buddies road bikes.
Normally I'd say go with as skinny of tire as your comfortable with and will work with your rim because you'll have less friction from the ground so you should be a little faster.

Just my 2c

Conti Sport Contact, Panaracer T-serv or Schwalbe Racer for that extra .2mph between stop signs.

The paselas have pretty low rolling resistance - I've worn out a few pairs of these in 26x1.5. Sport contacts are faster, but heavier and wear out relatively quickly. I was getting less than 2000miles out of Sport contacts, and over 4500 from Paselas. Don't overinflate, just stick to the recommended maximum.

If you go from 1.9" big apples to 1.26", you might find the handling affected. that big a shift in tyre size will change the trail.

I would say that if you are on a stop start route you'll benefit greatly from a lighter tyre. Takes much less energy to accelerate.

OTOH, if you are mostly cruising on the open road, tyre weight doesn't matter so much.

I am really happy w/ my 2.0 big apples. I am open to considering 2.0 or even (gasp) 1.5 marathon supremes. But I haven't been convinced that they can run at as low a pressure as the apples (obviously the 1.5s wouldn't but...)

you will go slower with studded tires. You will go faster on tires with air in them. You still have to stop at lights/signs etc. I'd go with the marathon supreme's with reflective sidewalls. I also like the conti contacts. If you go really light/slick, you will go a bit faster...until you have to change a flat. This is my personal bad luck experience recommendation.