I opted out of site-specific radiation (5 sessions over 10 days). I had an OncotypeDX 'risk of recurrence' score of 3% so no chemo was recommended. I tried an aromotase inhibitor, twice, with resulting side effects that were, for me, not tolerable for such a low recurrence risk.

If the number 16 you cite is your OncotypeDX 'risk of recurrence' number (not the trade-marked Recurrence Score on your report), you can roughly calculate your predicted risk of recurrence as around 30% if you do NOT take aromatase inhibitors or tamoxifen according to the OncotypeDX algorithm. I would consider that a high enough risk that I would at least try the aromatase inhibitors and get an endocrinologist or rheumatologist to help monitor osteoporosis.
It's a personal decision that a lot of us are faced with so you might also get a second oncologist to opine. There may be something that she/he sees in clinical evaluation to suggest a prognosis based on real-world oncology experience.

I would likely at least seriously consider the short-course radiation. Nothing is risk-free but I've known people who've had it without side effects or complications. But that too would be something I'd get a second opinion about.