Analysis :: DAX With IF Statement Very Slow

I have been trying to optimize a few DAX calculations that I have in my cube and ran into this problem Basically my DAX Measure 

Counterparty Collateral Base DKK:=
[Counterparty Collateral Contracts DKK (filtered)] 
+ 
CALCULATE(-[Account Balances DKK], Accounts[Counterpart Type ID] <> 8, Accounts[ContractTypeID] <> 14, Accounts[ContractTypeID] <> 16)
is pretty fast,
whereas as soon as I change the 2nd part to only add Account Balance if its>0, it takes ages i.e.
Counterparty Collateral Base DKK:=
[Counterparty Collateral Contracts DKK (filtered)] 
+ 
IF(CALCULATE(-[Account Balances DKK], Accounts[Counterpart Type ID] <> 8, Accounts[ContractTypeID] <> 14, Accounts[ContractTypeID] <> 16)>0,
CALCULATE(-[Account Balances DKK], Accounts[Counterpart Type ID] <> 8, Accounts[ContractTypeID] <> 14, Accounts[ContractTypeID] <> 16),0)

Offcourse because I check every row I suppose with that "if" statement. Question is how do I improve it?
B
y the Way: [Account Balances DKK] is in the table - Account Balances
                    [Counterparty Collateral Contracts DKK (filtered)]  is in the table- Open Positions

This calculated measure [Counterparty Collateral Base DKK] is in Open Positions.And the query in MDX, that I run to pull this measure, looks like
 
select {[Measures].[Counterparty Collateral Base DKK]
}on 0,
Non Empty {[Accounts].[Counterpart ID].children
  *[Base Currencies].[Currency Code].children
  *[Products].[Product Name].children
  } on 1
from [model]
where [Dates].[Date].&[2015-06-30T00:00:00]

The requirement is such that I have to add the measures in two separate tables.How can I improve the performance when adding the filter?