I need to cut 1 ceramic tile 15" long.Home depot or lowes will not do it.
I could buy a inexpensive tile cutter for $20.00. I have a lot of saws.
7 1/4 circular saw but the blade is for wood. Have a 10" miter saw, blade only cuts wood.
Also I a have a 4 1/2" angle grinder with a masonry wheel. I wonder what to do?

Rent a tile cutter from HD or Lowe's or buy one of the cutters that cuts like a glass cutter. I bought a 7" with a diamond blade on Craigslist for $40, used it for 3 bathrooms, a kitchen and a basement, then sold it on CL for $40.

I would give it a shot with your angle grinder. Test a scrap first if possible.