What a gorgeous coin. These coins are truly an elegant merge of history, art, and precious metal. Nice!
Now don't let anyone tell you that your 1915 Austrian 100 corona was minted in 1915. It wasn't. Austria is quite famous for re-strike coins, that is, coins produced much later than the date on the coin indicates. The most notable example is the Maria Theresa thaler which is dated 1780 but could have been struck last week!
Austrian 100 coronas dated 1915 are bullion coins. That is, they are coins produced so people can easily invest in gold bullion. They are worth their weight in gold. Each coin contains 0.98 troy ounces of pure gold. So, to find the current value, go to kitco.com and find out what the current price of gold is. At this writing, gold is trading at $1718 US dollars per troy ounce, and a 1915 Austrian 100 corona is worth 0.98 x 1718 = $1684. But tomorrow it will be different, so be sure to look it up.
Now, if you have a 100 corona dated before 1915, you have a numismatic (coin collector) coin, not a bullion coin. The value of numismatic coins depends on gold value plus collector demand, as follows:
100 CORONAS DATED 1915 (bullion coins):
worn: gold value
average circulated: gold value
well preserved: gold value
fully uncirculated: gold value + $10 US dollars
100 CORONAS DATED BEFORE 1915 (numismatic coins):
worn: gold value
average circulated: gold value + $20 US dollars
well preserved: gold value + $100
fully uncirculated: gold value + $300
If you are a coin collector, buy Austrian 100 coronas for your collection. If you are a bullion investor, buy 1915 Austrian 100 coronas for your portfolio. But (this is important):
DO NOT MIX BULLION INVESTING WITH COIN COLLECTING
you expose yourself to fast-talking shysters.