Hi Dave!
I'm with Tyson...I wish I had a room that nice for a model RR!
This is just my personal opinion, & reflects my favorite style of operation...if I was modeling in HO, & had space along a 16' wall, then I would have one dandy little switching layout. That way, I could avoid reverse loops, could keep the curves broad enough to handle any size equipment, & have more usable space for yard trackage, & scenery.
But that's just me.
If you prefer to keep the loops at the ends, then Tyson's right, you might get away with 22" curves, but this will bring the trains precariously close to the edge of the layout...I think 20" is more realistic. (are you using flextrack, or sectional?)
I have a simple rule of thumb that I follow when it comes to curves...
In HO scale, if the curves are under 24", then the only thing that's going to look, & operate well on them are 4-axle diesels (you could also include small steam locos), & 40'-50' rolling stock.
The bottom line is, though, for you to get it so that it works for you, & you enjoy yourself!
Good luck...keep us posted on your progress!