A Becquerel is 1 atomic disintegration per second.
1.5 Bq/kg means that 3 atoms of the ~10^24 (1 with 24 zeroes after it) in a kilogram of material disintegrates every 2 seconds.
This is utterly insignificant.
The national Academy of Science BEIR VII report as well as early research by John Gofman reveals that all increases of radiation result in increases in risks of cancer and other diseases. Low levels of radiation are hazardous. Raising levels of Strontium-90 is unhealthy for humans. And I think part of the issue here is that if Strontium-90 is present 245km from the plant- it’s present in even higher levels elsewhere in Japan.