Thanks LoyceV, I took your advice and just checked the balance. And I was pleasantly surprised. No I am not a millionaire but a few thousand dollar was much more than I had expected.
Congratulations on your new small fortune 
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What do you guys think: hold on to them a bit longer and see what happens? Since I invested only a few dollars back then there is not much risk in keeping them and see what happens in the future. What would you do in my position?
When you say there's not much risk because of your low initial investment, you're looking at it the wrong way. Your initial investment is irrelevant, the current value is what you're risking now. Price Speculation is another board though.I can only advice you what I would do, given my current knowledge: take some profit: sell a part of your coins. Sell enough to have something in your hands if the price drops, but keep enough to still have enough if the price goes up tenfold. Maybe sell 10-20% now, and do the same if the price doubles again?
Just don't panic sell if the price drops 30%, that happens quite often. Until now you've been oblivious when this happened, until now Bitcoin always recovered again.
One last thing: if you sell a part, make sure you store the remaining amount in a safe place again. If your computer is clean and trusted you can import the key. Electrum was mentioned already. Make sure you keep track of where your change goes if you just import your private key.
A modern Electrum by default asks you to write down a 12 word seed phrase. After this, you can sweep your private key instead of importing it. This takes care of your change addresses, and the seed words are enough to backup all your future transactions.