I know that the 110 goes  a bit deeper but is it worth having both,if I can get by with one? Which one?

I prefer to go with deeper diving baits.  Adjust your retrieve speed to regulate the swim depth. 

I only use the 110...I bought one 115 and tried it, I can get away with the 110 in shallow water with no issues...I ended up getting rid of the 115

Two baits that were designed to do different things.  The 110 is a suspending cold water, pre-spawn type bait, fishes about 6-8 ft deep.  The 115 besides being longer is also more bulky and floats, some people use it like a twitch bait, it was designed to fish over shallow beds when the fish are protecting them in full on spawn mode.  

If I was only going to buy 1, it would be the 110.

Check out a couple of Mike McClelland video's and he will tell you all about his thoughts on these baits.

 

I like the 110, but I like the McRip better!

The 115 is a floating bait and therefore can be more effective during warm water periods. I think if you are looking at using a bait just for spring fishing then you have to go 110 since it is a suspending bait.