Checking this out for an answer brings up two concepts and the answer to your question is that it depends on why your isp is throttling you.
You can get throttled ( so to speak ) because you’ve exceeded the limit by the amount you have downloaded, or by the content of what you’ve downloaded. Some isp’s it seems object to some streaming services and when it is discovered they throttle your speed down. Others go by the total amount you have downloaded.
In the first instance a VPN would assist in stopping them finding out that your streaming because when they checked the data they couldn’t identify it as a streaming service.
In the second instance a VPN could only assist you if it offered data compression, which would cut down the total amount passed over your connection, however it introduces an overhead of its own.
Neither is a complete solution to your problem, but may lend a helping hand.
Info from HERE and HERE.
Also, I’ve just had an email from Mozilla about how Firefox now has its own VPN. Maybe worth a look if your throttling is content based.
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