Hello there. I hope you had a good day so far.
I have an interior scene, a school scene and all my wall vars, floors and ceilings are seprate from each other and really it makes i think more than 250 or 500 objects just for that and for all of them I used one trim sheet. So can I now combine floors that are in a same coridor so I have a lower draw calls or that can make problems?
Thank you guys.
and sorry about grammer mistakes.
Просто сгруппируй по этажам. Не вижу проблемы. Или сделай саблвла для каждого этажа
Thanks 
Assuming you were told to use the actor merge system to manually aggregate some things.
I wouldnt necessarily go overboard with this unless the engine is having difficulty rendering.
Generally, more parts leads to more draw calls, but also allow for better optimization in terms of occlusion (things unseen won’t be rendered/won’t cost).
If you are using a kit of some sort, with 1m wall/floor/ceiling chunks, then yes. You need to reduce the amount of calls by merging actors and/or instancing things.
Its common to make different sets of merged actors from a modular kit, and subsequently re-use the merged actors as instances to create the working level.
Also, its common to just merge and re-use whole rooms, it just depends on how one needs to access things, and how collision/interaction needs to work for the game.
Thanks. So I just merge things depends on Environment parts like I merge floors and ceiling on a small room and merge every 2 tile floors in a large corridor right?
Depends on how many drawcalls you can comfortably handle on the lowest end system you wish to support.
Merging too much will negate occlusion, so the whole mesh will always be loaded.
If that is just one regular sized room it would likely be fine.
If it is a 300m^2 hangar it likely would not.
Thank you. It helps me so mush. 