Nitrate is a end product of the waste your fish produce, it has some effect, such that you don't want a lot more than 20ppm but it isn't going to kill your fish. Ammonia and nitrite are the less oxidized version of Nitrate and those two do damage to gills and in that way are hard on your fish. A tank that shows either ammonia or nitrite are evidence that there is insufficient "cycle", which refers to the bacterium that use those two toxic forms and change it in two steps to nitrate.
Any time you test and see ammonia or nitrite do water changes to get the levels down. If you are doing regular weekly water changes it will be no problem to do two or more 50% changes in a day if needed until you don't have any ammonia or nitrite readings.
Now for the regular maintenance part. That Nitrate isn't a big problem but if it gets to high it can be evidence of other issues which are solved by doing water changes. In a tank with no plants nitrate is something easily tested for that is used to give you some idea where you stand on things you can't easily test for (buffering, having minerals available to your fish, removal of hormones and other non nitrogenous pollutants etc.) You don't have to understand all that as long as you keep Nitrates down with water changes.
I suggest that you test your source water for a baseline nitrate level. A good level to keep nitrates within is 20 ppm, but if your tap starts with 15ppm it would be asking a lot of you to manage that, so a compromise is to keep your tank nitrate levels to less than 20 ppm more than what your source water has in it. So if your tap has that 15 ppm of nitrate you would be doing a 50% water change when the level in the tank reached 35 ppm nitrate. That would put you down to 25ppm and you have some unknown time that the levels will creep back up to 35ppm. That rate depends on how many fish you have and how much you feed. It might take 10 days or it could take 5 or less. Do the tests at first and the tank will tell you how often it needs a water change given these guidelines.
If you are dedicated you might not care if it needs a change every few days, but that does leave you with a very small margin of error as to what could go wrong. It can be fun to have that much in a tank, but it is work and should your pump fail you don't have as much leeway time to catch a problem because things build up faster.
Success wise it is easier to have extra wiggle room in your maintenance schedule. If your tank takes two weeks to get to 20 ppm nitrate more than tap and you do weekly water changes you will have an easier time getting away with things like going on vacation for a week or even two weeks.
