こんな感じのことでしょうか｡

Option Explicit

'//--------------------------------------------
Sub MainSample()
'//--------------------------------------------
 Range("B16").Value = StrSumIf(Range("B1:B15"), "【P】")
 Range("C16").Value = StrSumIf(Range("C1:C15"), "【P】")
End Sub

'//--------------------------------------------
Function StrSumIf(範囲 As Range, 文字列 As String)
'//--------------------------------------------
 StrSumIf = 0
 Dim ｾﾙ As Range
 Dim 分割結果
 For Each ｾﾙ In 範囲
 If InStr(ｾﾙ.Value, 文字列) Then
 分割結果 = Split(ｾﾙ.Value, "-")
 If UBound(分割結果) = 1 Then
 If IsNumeric(分割結果(1)) Then StrSumIf = StrSumIf + CDbl(分割結果(1))
 End If
 End If
 Next
End Function

ｺｰﾄﾞを標準ﾓｼﾞｭｰﾙにおけば､B16 に直接下記のように書いても使えます｡

=StrSumIf(B1:B15, "【P】")

標準ﾓｼﾞｭｰﾙに以下のｿｰｽを貼りつけてください｡

Function keykazan(ar As Range, st As String)

 Dim c As Range
 
 Dim kekka As Long
 
 kekka = 0
 
 For Each c In ar
 d = c.Value
 If InStr(d, st) > 0 Then
 kekka = kekka + 数値取得(c)
 End If
 Next c

 keykazan = kekka

End Function

Function 数値取得(r As Range)
 Dim myStr As String
 Dim myN As String
 Dim i As Long
 For i = 1 To Len(r.Value)
 myStr = Mid(r.Value, i, 1)
 If myStr Like "[0-9]" Then
 myN = myN & myStr
 End If
 Next i
 If IsNumeric(myN) Then
 数値取得 = myN * 1
 Else
 数値取得 = ""
 End If
End Function

使い方
ｾﾙに
=keykazan(B1:B15,"【P】-")
と入れれば､B1からB15の間で 【P】-を含む文字列がある数値を加算します｡