The measured difference is 0.4 years in this UK dataset.
MeasureChihuahuaPomeranian
UK median survival11.8 years12.2 years
95% confidence interval11.5–11.9 years12–12.5 years
Source records14,6364,111
Descriptive result
Pomeranian 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.