I'm super behind the idea of UBI, but I don't think two test sets of only 15 people is really gonna tell us much other than '30 people have been given a pay rise'.
We really need to answer questions like:
How will the market react? Do we need to put in some sort of legislation to stop price hikes if everyone has more disposable income?
Do we need to set certain 'essential' goods and services to a certain price to match the UBI payment?
How does this effect the UK's standing in the global economy?
To answer this we need a way bigger test population, like a whole town or a county.
I think that this is to collect data so we could have good arguments supported by data when we will finally come to fight for UBI for everyone. But yeah, this test sample should be at least 5 times bigger to make data actually reliable.