For myself, I would be leery of a hybrid as a touring bike. I think of hybrids as "mountain bike lights". Okay, all you hybrid lovers can attack at will. But I thought hybrids were for people who wanted an upright seating position, a triple chainring, smooth-rolling 700 tires, maybe lightweight suspension forks for a plush ride, and an overall-lightweight bike (light because it doesn't have to be overly strong.) That's great for recreational riding on pavement and crushed rock trails. But carrying a load and humping it up over steep roads puts a lot of stress on a bike (doesn' it?) I know people have toured successfully on hybrids and they work great. If you have a hybrid, don't be afraid to tour on it, it will probably be a fine choice. But if you are thinking about purchasing a bike with loaded touring in mind, I think you'd be better off buying a touring bike. You'd know that the frame, wheels, and components were selected with (hopefully) loaded touring in mind.

I'm not sure there's a bike that will be perfect for both gravel and dirt forest service roads and also normal touring on paved roads. I think you'll either need two bikes (expensive!) or some sort of compromise.

I often ride on rough roads with my LHT. It's not a big deal. I have to expend more effort on watching where I put my wheels, and be really careful in loose gravel, but it's doable. Having bigger tires helps. I have Schwalbe 32's. If I were on 23's I'd need to be way more careful. However, when I'm carrying a full touring load I'm really leery of rough surfaces. The worst problem I've had on tour is broken rear spokes, and I don't want anymore. I'm paranoid that I'm going to hit a bump and hear that horrible 'PING' sound.

You can also tour successfully on a mountain bike. I'd prefer a hardtail because you wouldn't need the added weight of rear suspension for touring. A bike with no suspension at all might be even better for the same reason. Anyway, put some narrower tires on your mountain bike, some bar ends for more hand positions, figure out a way to attach racks (or use a trailer) and you're good to go.

So, either way, it's a compromise. Get a touring bike which will be great on pavement and okay on gravel, or a mountain bike which will be great on gravel and okay on pavement.

If I were going to tour on a lot of gravel and dirt roads, I think I'd either take my mountain bike or a trailer. The mountain bike is strong, has even fatter tires, and the 26" wheels are a bit stronger. The trailer distributes the load over two wheels (the bike's rear wheel and the trailer's wheel) and is less likely to break a spoke (or so I've been told; I've never taken my trailer on a tour on dirt roads.) I might even opt for the BOB with suspension, although they're awfully expensive.

For $1500 you might be able to get a complete LHT for paved roads, and an old no-suspension mountain bike off Ebay for dirt roads.

One other consideration (there are many others, but this is one.) You can make a lot of changes with wheels, tires, gearing, brakes, saddle, stem, handlebars, etc. You can really dial things in the way you want. You can't do anything about the frame. You can't make the chainstays any longer. If you have big feet and your heels hit your rear panniers, your only option is to slide the panniers back further on the rack, which doesn't help your handling. You also can't make the bottom bracket any higher, although I can't see that being much of an issue. Maybe I'm wrong, but I can't see myself touring anyplace where I'll be riding over boulders, fallen-down logs, etc. And you can't make the frame any stronger. I think breaking a frame is rare, but I've had to deal with a bike that shimmied terribly at speed with a load. It was scary because I felt like I might lose control, and I was also worried that something might vibrate loose or break with all that whipping from side to side.

There are lots of things to consider, but having $1500 to spend gives you options. Will part of that sum be going to racks, panniers, etc? That will change things a bit, though there are inexpensive but acceptable choices.