Both Perl/Tk and Tcl/Tk use the same Tk codebase, so there will be no difference there. Typically perl seems to be faster at many things than tcl, so your grograms may run faster in the perl/Tk system. I do not know if the perl/Gtk toolkit would be faster, but it would be more complex to program for simple stuff.

I have used Tcl/Tk graphical apps and never noticed an app that takes forever to load. To determine whether it is your program or a Tcl/Tk problem, try running wish from the command line.