How to speed up json parsing with a lot of nesting?

Question

PHP

There is a json ~ 12mb in size. And it has 5 levels of nesting.
City
-Housing complex
-House
---Entrance
----Apartment The
file is taken via FTP and parsed into the database. It is parsed rather clumsily - foreach for each level of nesting. It takes about 10 minutes.
How can I speed up parsing? Any ways, for example, write a parser in C. Or run multiple foreach in parallel? What other tricks are there? More or less useful could not be googled. Thank you.