The phrase "stratospheric levels" means extremely high or elevated levels, similar to how the stratosphere in the Earth's atmosphere is higher than the lower parts of the atmosphere. Full definition
The only worry now, with house prices reaching stratospheric levels, is that it has all come too late. (canadianbusiness.com)
The Inevitable Fall After Bitcoin and Ethereum prices rocketed to stratospheric levels in late 2017, recent falls over the last few weeks have hit fast and hard. (cryptyk.io)