the formica is too slick and non porus to cause tile to adhere to it. Removing is the best option and one for longetivity.
Removing is fairly easy. get a stiff putty scraper and just start prying off. On especially hard areas, heat the putty knife slightly and it will cut through the contact glue like butter. Watch what your doing if you elect this option.
Try to get large sections so that it will peel off instead of taking off small pieces.