Obviously there will always be certain computer minimum requirements for any game..
but I've made many Layouts far bigger than 6000x6000
and loaded entirely with hundreds of objects and up to 20 or so parallax layers
and it works fine
but Testing is important....If it runs badly on your computer then You may want to downgrade the number of objects...
Generally Tilemaps use less processing power but not always...
It depends also on the number of Collision calls you are making per tick