> SHELL=/bin/shell
> 15 * * * * /homes/mcmahill/tst.sh >/dev/null 2>&1

O'Reilly's ``Essential System Administration'' writes the following
example:

30 3 * * 1 /bin/csh /usr/lib/uucp/uu.weekly 2>&1 >/dev/null

This example seems have the same intention of yours and does have
different redirection from yours which seems correct for /bin/sh and
should work.

It would be help that correcting ``SHELL=...'' and/or examining
behaviors of redirection of shells.

Masao