Excel 2013 File having multiple formulas taking too much time to Open - Pls Help!!

Dear Gurus,

My main file is having around 30 columns and all the 30 columns are filled with data fetched from four different files using vlookup and other formulas.

File 1 Contains 8K line items with 20 columns
File 2 Contains 8K line items with 40 columns
File 3 Contains 12K line items with 20 columns
File 4 Contains 3K line items with 40 columns

When I open the main file it is taking around 15 to 20 minutes to open the file. It shows (Calculating: (4 PROCESSOR(S)): 0%)....

The following formulas are used in the main file...
=MID(E24,MIN(SEARCH({0,1,2,3,4,5,6,7,8,9},E24&"0123456789")),4)
=INDEX($C$2:$C$11,MATCH(F2&" "&G2,INDEX($A$2:$A$11&" "&$B$2:$B$11,0),0))
=VLOOKUP(B2,File1.xlsx!$A:$B,2,FALSE)
=IFERROR(VLOOKUP(B2,File2!D:E,2,FALSE)," ")
=IFERROR(VLOOKUP(NUMBERVALUE(N2),File3.xls!$B:$T,19,FALSE),"")
=NUMBERVALUE(Z2)+NUMBERVALUE(AA2)
=IFERROR(VLOOKUP(NUMBERVALUE(N2),File4.xls!$B:$E,4,FALSE),"")
=TRIM(A2)
=IF(L2=M2,M2,L2)

Please help me to resolve this problem?

Regards,
Suresh