Open dosbox_swarrior.conf and edit:

language=
machine=svga_s3
captures=capture
memsize=32

to:

language=
machine=svga_s3
captures=capture
memsize=64

Unlike Duke Nukem 3D memory limit in Shadow Warrior is not static or optimized at all, so sometimes memory overflow occurs. 32 should work but at random instances too much stuff is rendered at once and this game itself don't have any internal limit to prevent that, so usually setting more memory in dosbox make these freezes less frequent.