[MunkDev]

function WorldQuestPinMixin:OnMouseEnter()
    WorldMap_HijackTooltip(self:GetMap());
 
    TaskPOI_OnEnter(self);
end

function WorldMap_HijackTooltip(owner)
    WorldMapTooltip:SetParent(owner);
    WorldMapTooltip:SetFrameStrata("TOOLTIP");
 
    for i, tooltip in ipairs(WorldMapTooltip.ItemTooltip.Tooltip.shoppingTooltips) do
        tooltip:SetParent(owner);
        tooltip:SetFrameStrata("TOOLTIP");
    end
end

function TaskPOI_OnEnter(self)
    WorldMapTooltip:SetOwner(self, "ANCHOR_RIGHT");
 
    if ( not HaveQuestData(self.questID) ) then
        WorldMapTooltip:SetText(RETRIEVING_DATA, RED_FONT_COLOR.r, RED_FONT_COLOR.g, RED_FONT_COLOR.b);
        WorldMapTooltip:Show();
        return;
    end
 
    local title, factionID, capped = C_TaskQuest.GetQuestInfoByQuestID(self.questID);
    if ( self.worldQuest ) then
        local tagID, tagName, worldQuestType, rarity, isElite, tradeskillLineIndex = GetQuestTagInfo(self.questID);
        local color = WORLD_QUEST_QUALITY_COLORS[rarity];
        WorldMapTooltip:SetText(title, color.r, color.g, color.b);
        QuestUtils_AddQuestTypeToTooltip(WorldMapTooltip, self.questID, NORMAL_FONT_COLOR);
 
        if ( factionID ) then
            local factionName = GetFactionInfoByID(factionID);
            if ( factionName ) then
                if (capped) then
                    WorldMapTooltip:AddLine(factionName, GRAY_FONT_COLOR:GetRGB());
                else
                    WorldMapTooltip:AddLine(factionName);
                end
            end
        end
 
        WorldMap_AddQuestTimeToTooltip(self.questID);
    else
        WorldMapTooltip:SetText(title);
    end
 
    for objectiveIndex = 1, self.numObjectives do
        local objectiveText, objectiveType, finished = GetQuestObjectiveInfo(self.questID, objectiveIndex, false);
        if ( objectiveText and #objectiveText > 0 ) then
            local color = finished and GRAY_FONT_COLOR or HIGHLIGHT_FONT_COLOR;
            WorldMapTooltip:AddLine(QUEST_DASH .. objectiveText, color.r, color.g, color.b, true);
        end
    end
 
    local percent = C_TaskQuest.GetQuestProgressBarInfo(self.questID);
    if ( percent ) then
        GameTooltip_InsertFrame(WorldMapTooltip, WorldMapTaskTooltipStatusBar);
        WorldMapTaskTooltipStatusBar.Bar:SetValue(percent);
        WorldMapTaskTooltipStatusBar.Bar.Label:SetFormattedText(PERCENTAGE_STRING, percent);
    end
 
    WorldMap_AddQuestRewardsToTooltip(self.questID);
 
    if ( self.worldQuest and WorldMapTooltip.AddDebugWorldQuestInfo ) then
        WorldMapTooltip:AddDebugWorldQuestInfo(self.questID);
    end
 
    WorldMapTooltip:Show();
    WorldMapTooltip.recalculatePadding = true;
end

-- from WorldMapTooltip in WorldMapFrame.xml
    <OnUpdate>
        if ( self.recalculatePadding ) then
            self.recalculatePadding = nil;
            WorldMapTooltip_CalculatePadding();
        end
        self.updateTooltip = (self.updateTooltip or TOOLTIP_UPDATE_TIME) - elapsed;
        if ( self.updateTooltip > 0 ) then
            return;
        end
        self.updateTooltip = TOOLTIP_UPDATE_TIME;
 
        local owner = self:GetOwner();
        if ( owner and owner.UpdateTooltip ) then
            owner:UpdateTooltip();
        end
    </OnUpdate>

All this stuff is running every 0.2 seconds on your game client, so I'm not surprised it causes your FPS to drop.