Pls How can I make 16F877A use 15MHz Xtal

[skimask]

My understanding is that to use 15 MHz crystal i need to include
DEFINE OSC 15
at the top of my pic basic pro codes
and that I needed to edit the 16F877A.INC file on my C: drive and replace XT_OSC with HS_OSC.
I have done this. Is there anything I am not doing? Thanks

XT vs. HS. Check the datasheets
You have to reconfigure your PIC to run the 15mhz oscillator.

And check your PBP manual for the correct use of:
DEFINE OSC 15