"Sporting" barrels are usually flat ribbed, and trap barrels usually have higher ribs. Point of impact is what your after. For trap, you would probably want a set of barrels that shoots a little high for you, 60/40 or more, but only you will know what you need. If you have an adjustible comb, you can play with that regardless of what type of barrels you buy. I'd go to a gun shop that has some models on the rack and pull them up, or see if they will allow you to snap various barrels on your frame and see what site picture you see. There are various barrel weights available as well. Good luck on that one, it takes a while to determine best barrel weight (say for doubles), it's all about smoooooothness! I shoot both trap and sporting with an MX-8 O/U, flat rib, 32" and just adjust my comb from doubles to sporting. Not bragging, but I'm AA27AA and Class AA on sporting. Also shoot the O/U on singles as well. If it works for me could work for you, but.....everyones different!
For your MX15 you are looking for a step rib or ramp rib MX 8 or MX 14 barrel. Any of the adj rib barrels & DB 81, as stated will require you to move the comb beween the unsingle & O/U. Many sporting barrels have no side ribs or ventilated side ribs but can be found with the proper rib height. The side ribs really only affect weight and is really no big deal. Good luck, DGG