Mongodb geographical location is slow to query by index.

I want to find a point in a circle on a sphere and execute the command:

db.places.find( { loc :
            { $geoWithin :
                { $centerSphere :
                   [ [ -88 , 30 ] , 10 / 3963.2 ]
           } } } ).explain()

found that it took five or six seconds to query the results.
nReturned=totalKeysExamined & totalDocsExamined
nReturned=390000 totalKeysExamined = 430132 totalDocsExamined = 430013
loc has added the 2dsphere index. The total amount of data is only more than 2 million pieces of data. I don"t understand why the query results are so slow.

Mar.11,2021
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e5448f-4529b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e5448f-4529b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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