Improve performance on native sql query - postgresql

Question

I'm trying to build a location-based application in Java EE, which returns providers from a certain radius given coordinates as input. As I use JPA, I couldn't find a solution to querying the database with a named query as it doesn't support functions like Sin, Cos etc. I found a nice read here, sql-haversine, where I could use a native query instead. The query executes fast (33 ms) on the database (Postgres), but very slow when executed from the application (> 800 ms).
Is there a way to speed things up, from the application end, or do you have to use something like a stored procedure in the database.
My method looks like this:
#SuppressWarnings("unchecked")
public List<Company> findCompaniesByProximity(Coordinate coordinate, int distance) {
double latitude = coordinate.getLatitude();
double longitude = coordinate.getLongitude();
String sql = "SELECT * FROM ("
+ "SELECT *, c.distance_unit * DEGREES(ACOS(COS(RADIANS(c.lat)) * COS(RADIANS(companies.latitude)) * "
+ "COS(RADIANS(c.lng) - RADIANS(companies.longitude)) + SIN(RADIANS(c.lat)) * SIN(RADIANS(companies.latitude)))"
+ ") AS distance "
+ "FROM Companies "
+ "JOIN (SELECT ?1 AS lat, ?2 AS lng, ?3 AS search_radius, 111.045 AS distance_unit) "
+ "AS c ON 1=1 "
+ "WHERE companies.latitude "
+ "BETWEEN c.lat - (c.search_radius / c.distance_unit) "
+ "AND c.lat + (c.search_radius / c.distance_unit) "
+ "AND companies.longitude "
+ "BETWEEN c.lng - (c.search_radius / (c.distance_unit * COS(RADIANS(c.lat)))) "
+ "AND c.lng + (c.search_radius / (c.distance_unit * COS(RADIANS(c.lat))))"
+ ") AS proximity "
+ "WHERE distance <= search_radius "
+ "ORDER BY distance "
+ "LIMIT 25";
List<Company> companies = null;
try {
Query query = em.createNativeQuery(sql, Company.class);
query.setParameter(1, latitude);
query.setParameter(2, longitude);
query.setParameter(3, distance / 1000.0);
companies = (List<Company>) query.getResultList();
} catch (IllegalArgumentException e) {
System.err.println("Argument is invalid " + e);
} catch (PersistenceException e) {
System.err.println("PersistenceException: " + e.getMessage());
}
return companies;
}
The method is called from a singleton EJB, and I'm using Payara server with Postgres and EclipseLink. Everything is called locally so I thought the connection to database would be much faster. Iv'e also tried the postgres earthdistance extension, but it was even slower ( > 1800 ms). I've quite new to programming and especially Java EE so I might have done something wrong along the way :)
Thanks, in advance.