“Rescued” a privet bonsai but it’s not greening up

Hi everyone. I’m a fairly competent gardener of outdoor plants but a complete newbie at bonsais.

10 days ago my husband spotted a heavily reduced bonsai in the garden centre, I had a sneaky bark check that the trunk and main branch was green underneath and felt fairly sure I could get it to come back - he’s always wanted a bonsai so decided to have a shot at rescuing it.

All its leaves were crispy and it has completely dried out. I gave the pot a good soak then put it under our velux where there’s plenty of light and a steady 18-20 degree temp.

So far there’s no sign of anything happening. The soil still seems very soggy, and I’m starting to see some mould growing on the top layer of soil.

Questions:

-is it normal for the soil to hold onto so much water, or should it be more free draining? 

-would it be happier outside (UK)? If so, would it prefer my greenhouse which is v hot and humid during the day at the moment, or a sunny sheltered spot elsewhere?

- I assume attempting to repot is a terrible idea?
 

I’m happy to be patient, but don’t want to accidentally make it less healthy than it already is! I haven’t removed the dried leaves, figured they’d fall in their own time and they’re not doing any harm, but equally I can take them off if there’s any benefit to doing so.

Any help appreciated!

The best place would be outside in a sheltered spot out of wind. The greenhouse will get too hot. It may be ok, but it may take a month or more to show.