Does a rental price go up? How to find out

The monthly figure you were quoted is almost never fixed for the life of a fifteen-year rental. That is not automatically a problem, and it is not something to discover on a bill. Here is how to find out what you actually agreed to.
The clause exists, and it has a name
Open your agreement and search for "adjustment", "escalation", "annual increase", or "CPI". It is usually one short paragraph and it is usually not near the price. If you cannot find your agreement, whoever you rent from is obliged to give you a copy on request, and asking for it is not a negotiation.
Four shapes the clause can take
An adjustment can be tied to inflation alone, to inflation plus a fixed percentage, to a flat percentage regardless of inflation, or left to the provider’s discretion up to some maximum. The wording that matters most is whether the number is a cap or a ceiling the provider may choose to reach. "We will increase by X" and "we may increase by up to X" are different promises, and only one of them is a promise.
Why the term length does the damage, not the percentage
A single-digit annual adjustment sounds small and it compounds. Over a fifteen-year plan an increase applied every year roughly doubles a monthly payment at 5% a year, and adds about half again at 3%. That is the arithmetic, not a claim about anybody. It is why the term and the cap matter more than the first year’s number, and why a total-cost comparison run on today’s monthly price is always too low.
The four questions worth answering
Is there an adjustment at all? Is it capped, or is the cap a maximum they may choose? How often does it apply, and on what date? And does anything else change, such as a service fee billed separately from the rental. Once you have those four you can compare any two offers honestly, including this one.
What Arctic’s adjustment is
An Arctic rental adjusts once a year, on the anniversary of your install. Increases are nominal in nature and tied to CPI and Arctic’s annual surcharge. The exact amount for every year is set out in your agreement before you sign, so the total over the full term is known on day one, and there is no other increase at any point in the plan. Purchase prices, financed or paid once, do not change at all.
If the answer you get is vague
A provider who will not put the adjustment in writing, or who answers with "it is only a dollar or two", is describing the first year rather than the clause. Ask for the clause. A company confident in its terms will send them, and one that will not has told you something useful for free.