Im moving to an apartment in town & im afraid my cats are to old for the trip,& change from outdoor to indoor.?

15 is elderly but not really old if your cats are healthy. When you move you will need to keep the cats confined in one room for a few weeks until they get used to the new smells, sounds and routine and then be very, very careful when going in or out of the apartment because they are used to going out of doorways. You will also need more litter boxes, i suggest 3, and they will get dirty much faster since your cats probably did most of their business outdoors. One of the cats may be much more determined to get outside than the other. I have one who is a speed demon when there is an open door so we usually shut her in her room when we leave so we don't have to try to slide through the door without her sneaking out when we get home. Give them enough time to get settled into the new home and be sure they have their old beds and dishes and anything else they are fond of from the old house when you move.