As others have said, "intrusive" is a subjective term. HP5 will give less grain if correctly exposed and developed in an ultra-fine-grain developer like Perceptol. It will show more grain if developed "normally" in a developer like ID-11, more grain still if developed in a product like Rodinal. As a rough guide, a correctly exposed and developed (ID-11) HP5 Plus neg will just show grain (visible to the naked eye) at 8x10", which is in no way to say that you can't enlarge it to 20x16" or any size you like.
It is probably better to approach the problem the other way round - what size prints do you want to make, and do you find visible grain disturbing? If at any given print size you find the grain unacceptable, even developing HP5 in Perceptol, then change either to Delta 400 (fabulously fine grain and sharpness IF you get the exposure and development spot on, otherwise a mess) or to a slower film like FP4.
Regards,
David