I have an optics ready MP15, looking to install a different handguard but would like to have one longer than the carbine length, need suggestions without going with a free-float handguard.

Magpul SL carbine. Gives almost the same length as a middy. Extends to the front end of the A2 sight post. Magpul MOE MVG MOE SL Handguard AR-15 Carbine Length Polymer Black

__________________
M60 442 642 637 686 686+ 629

If it's the optics ready sport 2, it's absent a fsb and has the goofy railed gb. Trash the gb, get a low profile gb and I'd suggest a free-floater. The FF provides many more options. Regardless, you'll need to replace the gb if you plan on using a longer handguard. Not knowing any better, I went through the same bs with my first ar, DPMS Oracle with the railed gb. After learning just enough to be dangerous, I modded it in a manner much more suitable to my liking. I continue to blame than gun for having turned this into a rather expensive little hobby.

Another user on the board was able to fit the Magpul SL carbine on his optics ready Sport, even with the "goofy railed gb".

There may be others that would fit as well, but as Bamashooter stated, if you replace the gas block with a low profile one and go to a free float hand guard, you will have a larger selection to choose from.