The letters of safe classification tell you the types of tools that your safe has been tested against, while the numbers refer to how long the safe can resist those break-in methods. TL refers to hand tools such as drill and saws. The 15 rating means that the safe is only theftproof against those tools for 15 net minutes. After 15 minutes of continuous exposure to hand tools, the safe becomes vulnerable. The lowest classification for a safe is TL-15.
A TL-30 safe can only resist the continuous use of hand tools for 30 minutes. After 30 minutes a burglar will be able to crack the safe.
TR refers to torches. So a safe with a TRTL-15 rating can resist both hand tools and torches for 15 net minutes.
A safe with a TRTL-30 rating has been tested against hand tools and torches. After 30 net minutes, the safe is not longer resistant to these types of theft methods.
A safe with a TRTL-60 rating is secure against hand tools and torches for 60 net minutes before becoming vulnerable to burglars.
While most homes do not require a safe that is resistant to explosives, a safe with a TXTL rating is resistant against all forms of theft devices including hand tools, torches and explosives. This is the highest classification of safe.