I would be very suprised if you needed 10-15hrs. With 300hrs and with a short break, you would hopefully find it fairly straightforward. If you stayed with Shoreham or dare I say, Lydd ,it may help with your subsequent flying as it's in your local area. I would also add that the FI/FE should have a good understanding of the EASA transition, as this will possibly be a licence change if you are outside the three year validity period. Please pm if I can help.