The measured difference is 3.2 years in this UK dataset.
MeasureSiameseBengal
UK life expectancy at age 011.69 years8.51 years
95% confidence interval10.56–12.82 years7.12–9.9 years
Source records8873
Descriptive result
Siamese has the higher point estimate in this source table. That does not prove that one individual animal will live longer, remain healthier or cost less than another.
Survival is not the same as healthspan.
The source comparison does not measure mobility, cognition, independence, lifetime veterinary cost or the effect of a supplement. Differences can reflect population composition, health, care and other confounding.