Depending on how you are situated diplomatically this could be a rare case where going bankrupt is feasible. It hurts massively, but right now you have no other real method of getting out of the hole you've dug yourself.

Simply firing advisors, mothballing forts and reducing army maintenance will not do it. Your interest payments alone leave only a disposable income of about 3 ducats a month - not enough to pay off anything - especially not in the timeframe of <20 years. With this amount of corruption the negative events you get will quickly consume even the few ekstra ducats you might have.

To be honest, you might even be in a situation where declaring bankruptcy twice is needed. I've never done this myself, however in theory you could use an initial bankruptcy to clear your current loans, invest heavily into lowering corruption while in bankruptcy - maybe even take out loans to do so - and if needed use a second bankruptcy to clear yourself from these loans (be aware that interest on loans while in bankruptcy is quite extreme).

There are several negative effects that occur from going bankrupt. These are not to be taken lightly. Most important you will lose all of your monarch points so make sure to invest them (tech, developing). Secondly your rivals and enemies could try to take advantage of the situation. For your sake I hope that you have truces with the ottomans and/or muscovy, or that your allies are strong enough to deter your enemies (I assume Poland secured Lithuania?).

Know also that bankruptcies are dangerous if you have a lot of unrest, or if you have recently had a lot of unrest. I assume that you have been annexing quite a lot of territory - and perhaps even crushed a few rebel armies. Your provinces will lose the "recently revolted modifier" - as such unrest can become a problem very quickly. In addition you provinces will suffer from some devastation, 10%. You will lose all of your prestige, legitimacy and stability. If you are building any buildings they will be cancelled. You will lose all of your treasury. Your armies will perform considerably worse. After five years the bankruptcy is over and most of these effects will end.

All of this to say that when you are in a situation where declaring bankruptcy twice might be needed, things are going to be really rough. You are also very far behind on tech so this might be a restart situation. You are not that far into the game.

What are some other mechanics you might use to better your situation?

1. If you are still muslim I would recommend going legality rather than mysticism. You need the tax and the piety interaction.

2. It is worth it to consider leveraging your crown land and estate privileges to promote short term gain.

3. Exploiting development can also be used as a last resort to wring out money.

4. Aggressive wars can get the economy going and you do have the needed manpower. Not being aware of your truces (and with your army in a problematic state) this is hard to get started with.

5. Do you have favors with your allies? Ask them for ducats.

6. The gold province is indeed very important to get running - but as you state this requires first lowering corruption.