multiple connection to one server

in vb6.0 i use about 20 client (use winsock) link to one server ,each client send picture(.jpg) to server ,if just only one client ,it can run.but when 20 client send picture at the same time ,the server can't run as one client link.
how i can improve this? in the server i use winsock array.this is my code:

Private Sub WsckServer_DataArrival(Index As Integer, ByVal bytesTotal As Long)
Dim sin() As Byte
On Error Resume Next
WsckServer(Index).GetData sin, vbByte 'receive the picture data
Call RealLise(sin, Index, True) 'process the data
DoEvents
Erase sin
End Sub

Public Sub RealLise(sa() As Byte, indexa As Integer, bolCS) '
On Error Resume Next
With jpgbuf(indexa)
For i = LBound(sa) To UBound(sa) ' i think the speed is very low
'each picture have a formate ffd8.................ffd9
'process each picture and show in the 20 image controls
next i
End With
End Sub

pleas help me. thinks.