Hey,

I recently bought a pretty nice fitness bike (deore xt groupset, kalkhoff carbon frame+ forks. Brand never got any attention for some reason and both are out-of-production items) for a really good price and I want to make it a bit more "road-ready", faster in the straights and all that.

Currently it has some 1.75in Schwalbe tires, not sure exactly what model but they aren't really MTB tires, they have a slim contact patch but are still quite wide and probably heavy. And the wheels, same as tires, have no clue what they are, probably some no-name ones because I literally found nothing on them. 28in size

So I thought to myself I could probably get some decent wheels and tires for it and that should make the bike lighter and probably faster, right?

I'm looking to spend as little as possible while still not buying some no-name components. Something that is similar to the Shimano Acera groupset, but just in the wheel world, cheap-ish but not total crap. Clincher, disk-ready, 30-32mm tires would be optimal.

Only concern is the fork. Since it can take really wide tires, it would probably look really weird running slim tires when it was made to take wide tires, plus I'm not entirely sure if it can take 700c wheels.

It is really hard to suggest anything without better info on your wheels...take a look at this and figure out what they are: Tire Sizing Systems

if they are 700c tires, then these: Review: Continental Grand Prix 4000s II 28mm tyres | road.cc are great and would still have some good comfort and grip while keeping a low rolling resistance.

as a thought, a new wheelset will be really really expensive (decent ones start around $350 HUNT 4Season Dura | Road Wheelset | 1696g | 21Deep 23Wide | £229 - PRE ? Hunt Bike Wheels that isn't too bad an option or some mavik aksiums, and great wheelsets can go into the many thousands of dollars). So, unless you have problems with your wheels going out of true, you can find new tires for them, and you are looking for exercise not beating land speed records, then a new set of tires might be all you need...

thanks, I'll try to find out what wheels I'm using first and then go from that

I note that you said "spend as little as possible." Good - you might consider "postponing" investment for a while... put 600 or so more miles on the bike thinking about what you'd like to change before dropping any serious bux, because your priorities may change in that time. Maybe you'll start to wish for a different saddle, maybe better shoes or a computer. New wheels & tires will make you somewhat faster, and you'll hear that "wheel upgrade is best bang for buck," But if you're in it for the workout, watts is watts. Fit and comfort may be the difference between 2 hours a week and 6 or more. New wheels will be a significant investment (at least $400, prob more) by the time you're done if you're spending wisely.

Upgrade your tires to make the road rides more enjoyable. Come back in a few thousand miles and you'll be ready to talk wheels. I recommend these (assuming 28in means 700c or 622):
Continental GP4000S II 28mm
Vittoria Voyager Hyper 32, 35, or 38mm