Speed of WinCC S5 CP1613 Driver Connection Slow

We are currently upgrading a COROS system to WinCC. We have duplicated the COROS type structures with templates to mimic COROS, this way the WinCC runs concurrently with the existing COROS. There are 15x S5 PLC's on a H1 bus (redundancy via star couplers). There are 6 COROS hosts (3 redundant pairs) and 10 clients (terminals).We have completed the change over of the first COROS redundant pair and are currently running the WinCC together with the 6 hosts.We are usingCP1613 cards for the communication with theWinCCSIMATIC S5 ETHERNET LAYER 4 DRIVER.
Our observation is that the WinCC runs slower than the COROS stations. The screens are identical copies and we find their update times are slighty slower (not really an issue), but its when we open a template (faceplate) and perform an action eg. switch a PID control from manual to continous mode that it takes up to 15 secs to respond with the action. On inspection in the PLC we notice the command (a number written in a DW)
'-------------------------------------------------------------------------
Dim Msg, Style, Title, Response
' WINCC:TAGNAME_SECTION_START
Const DW1 = ".DW1_ControlParameter"
Const DW5 = ".DW5_Inputs"
'WINCC:TAGNAME_SECTION_END
'-------------------------------------------------------------------------
'DW5 Bit 15 = INEX

If HMIRuntime.Tags("" & DW5 & "").Read And 2 ^ 15 Then

Style = vbOKOnly + vbExclamation
Msg = "Control switching is on EXTERNAL"
Title = "Input Disabled!"
Response = MsgBox(Msg, Style, Title)
Exit Sub
End If
'-------------------------------------------------------------------------
'If all conditions ok ask user if they are sure about their selection
Style = vbYesNo + vbExclamation
Msg = "Are you sure you want to select CONTROL"
Title = "Select CONTROL?"
Response = MsgBox(Msg, Style, Title)

If Response = vbYes Then
HMIRuntime.Tags("" & DW1 & "").Write 9
Else
Exit Sub
End If
'-------------------------------------------------------------------------
( We mostly use c scripts but were unable to work out how to make a mesage box pop up so we opted to use vb for the commands that require confirmation )

takes nearly 10 secs to arrive at the PLC, in COROS this happens in less than a second. If we place this template on a empty page the transmission occurs a lot faster (2 sec) so it tells us the busy page graphics (dynamics) is holding up the sending of the command. Is there a way from within WinCC to prioritize the command over the page updates? The WinCC PC's are Pentium IV with 2GB of memory. There are 25 screens with some screens having up to 50 items. When configuring our structure tags, we added all the elements from the DX in the PLC, which means there are tags we are not using currently but may use in the future. When using structures does WinCC read all the tags configured in the structure or just the ones that are requesting and update from the page?