If you are unable to withdraw, just keep trying. I started to sell off some of my solos now, just to get out completely before the collapse I have predicted... It took me 12 hours and a dozen tries but I just cleared out another $3k on top of the $15K I cleared out before the whole freeze thing started. Either the software is just buggy as hell, or else (more likely IMHO) GAW cannot allow you to withdraw coins it doesn't have.
I tried a lot of times to withdraw BTC but always same error...
Unable to process transaction at this timeI had the same error a dozen times over 12 hours. I tried every hour except when sleeping and it finally went through on my last try. If you believe GAW just has bugs, then file a support request and post in the support thread. If you believe that GAW lacks the coins to payout what is in is customers accounts, then support requests will be useless, you will just need to get lucky and wait until GAW has accumulted more coins from miner sales and whatever else it is doing to be able to pay you out. In the latter case, perseverance, timing and luck are required.
Also, again on the assumption that the issue is lack of sufficient coins to allow withdrawals as opposed to a software bug, you can try taking out smaller amounts too. You may not be able to get 15 BTC out but 1 BTC might work for example. Of course if its a software bug/issue, reducing the amount won't help you. I can only tell you that I got my BTC out after great effort and many attempts, using different amounts of withdrawal (e..g, not always emptying the account).
Another thing I experimented with successfully was buying on the market before withdrawing. Buy a few solos cheap, then try withdrawals again. That seemed to work though it maybe a coincidence. The hypothesis behind this strategy is rather cyncical, but it is based on a hypothesis (unproven) that GAW wants to keep its active customers happy, but is willing to stiff its customers who are exiting. One way to do that would be to prioritize withdrawals from customers who recently purchased miners. Again this is purely a hypothesis, but it has worked a couple of times for me and can't hurt to try it.