I could be totally wrong here however I would have thought the...

I could be totally wrong here however I would have thought the time premium for LEGO would be calculated relative to the LEG price and not the LEGO option price. Using the previous example of LEG @ 23c and LEGO @ 11c (8c intrinsic + 3c premium) the premium % relative to 23c is only 13% for just over 1 year until expiry rather than the 37.5% (3c/8c) which you have calculated.

With the 15c options being currently way in the money, the premium would factor in the time value until expiry (i.e. the return you could receive for the money you don't have to tie up in the phyisical) and the volatility of the stock. Given the stock has almost doubled in the past few weeks, I don't think a high volatility is unreasonable.

I previous held DEGO and could never understand why they traded for less than DEG when you added the strike price of 20c. Maybe it was liquidity that was the main issue.